IVF Horizons: Microfluidics

June 4, 2012Carole 1 Comment »

I am starting another new series called IVF Horizons which will be dedicated to reviewing what the new advances in IVF clinical therapies might be. Today’s topic is microfluidics, possibly the next new method for better fertilization and embryo culture.

What is microfluidics? Microfluidics is a technology based on the behavior of fluids at micro volumes. At tiny volumes, fluid flows in a smoother laminar fashion instead of the turbulent pattern seen at larger volumes. Viscosity and surface tension are the predominant forces at the microscale, creating a microenviroment which is conducive to  very rapid diffusion of nutrients.

These characteristics applied to the IVF system would allow gametes and embryos to have fresh culture medium in an enclosed micro-environment, without moving them to another dish with fresh medium. Moving gametes around via pipettes from dish to dish exposes them to shear forces and abrupt changes in the composition of their growth medium. These abrupt environmental  changes may shock the embryo’s system.

A microfluidics microenvironment in vitro appears to be more consistent with the natural system in the Fallopian tube where the fluid environment is continually in motion due to the movement of cilia along the surface. In vivo, the eggs and embryos are rolling around the surface allowing access to all sides of the egg/embryo for exposure to fresh medium. This natural motion may enhance fertilization or embryo development according to some studies  (Nir 2002 and Croxatto, 2002)

Interestingly, this technology nicknamed “laboratory-on-a-chip” has already been used for other microassay applications, because all the steps for detection of a biological signal/chemical/DNA amplification product  including sample handling, mixing, incubation, sorting, transport, interaction, and molecule detection can be performed on a tiny disposable surface quickly and inexpensively compared to current macroscale assays. The laminar flow that occurs in a microfluidics system allows parallel fluid streams to be manipulated independently to permit the delivery or sampling of particular molecules at particular times. Manipulation of streams of media can be used to introduce sperm to egg or remove cumulus cells from eggs or to change the medium surrounding an embryo as it grows.

Potential cost savings from these devices could come from the massive reduction in the volume of media needed per IVF case. Current human IVF culture media is superbly expensive, the champagne of culture medias. Tablespoons of some media can cost upwards of hundreds of dollars. If only microdrops are needed for the entire case, the cost savings would be enormous. Automation of the IVF system may not bode well for employment of embryologists since fewer manual tasks will be required as these become automated on the chip.

Polydimethylsiloxane (PDMS) is one material that is used to produce microfluidics devices for IVF because it is non-toxic, transparent, insulating, and permeable to gases, all desirable characteristics for material used to culture embryos. Initial studies from these materials suggest that PDMS is non-toxic to both gametes and embryos. This material is easily moldable and can be adhered to glass chips as necessary for some designs.

The principle of microfluidics has been employed to create micro-devices for sperm analysis and sorting. Small numbers of sperm are recovered which would certainly be adequate for ICSI, but the method would have to become much more efficient to achieve sperm yields from the ejaculate needed for applications such as intrauterine insemination (IUI).

Microfluidics has been employed to handle oocytes and gently remove the surrounding cumulus cells via suction in the microfluidics chamber. Studies using bovine eggs showed that 90% of eggs cleaved post-fertilization after removal of cumulus cells using this system. The time to remove cumulus cells was very short compared to manual removal, on average between 15-20 seconds per egg. Removal of cumulus cells by hand using hydrolytic enzymes and manual pipetting can take several minutes.

Initial studies with pig and mice eggs  demonstrated that IVF can be performed using a microfluidics chamber. One advantage of this system is that extremely small numbers of sperm can be used which is probably more similar to nature. In nature, there is a huge loss in number of sperm as the sperm travel from their initial site of deposit in the vagina, through the cervix, uterus and finally to meet the egg in the Fallopian tube. All along the way, weaker sperm are lost and the final number of sperm that reach the egg are very low. Estimates from previous studies suggest that only a 100 sperm may make it to the egg under natural conditions. Current IVF systems require between 2000 -50,000 sperm per egg, compared to the microfluidics system in which less than 1500 sperm are needed. Fertilization rates appear to improve as the sperm numbers decrease in the microfluidics system, perhaps due to the lower metabolic load (due to fewer sperm) driving  depletion of nutrients in the medium and fewer waste products produced by fewer sperm. Preliminary experiments suggest that very good fertilization rates can be achieved in the microfluidics system  with low sperm numbers similar to those found in nature.

Sequential culture systems were developed based on a better understanding of the changing nutritional needs of the developing embryo. Microfluidics technology has the potential to more gradually and gently change the nutritional environment of the embryo, more in keeping with the embryo’s needs.

Several companies are working to bring effective microfluidics “IVF lab on a chip” technologies to clinical use. I am aware of at least two companies but there are likely more.  Incept Biosystems, has used microfluidics technology to produce a prototype IVF device that has been used in clinical trials at four different IVF programs. Smart Biosystems is a Copenhagen, Denmark company that unveiled their  “IVF  lab-on-a-chip” product  IVF Lab-6 at this year’s ESHRE meeting at the end of the month. The company websites feature videos of these devices.  (I have no financial interest in any of these companies or devices.)

Another benefit of microfluidics culture may be that accurate real time sampling of the fluid around the embryo may become possible. The next “Holy Grail” of IVF is selection of implantation-capable embryos from a group of embryos to produce a viable pregnancy. Knowing which embryo has the juice to go the distance will eliminate the need to transfer more than one in the hopes of getting at least one to implant; reducing the incidence of multiple births from IVF.  Measurement of embryo metabolism has been suggested as one assay that may indicate the most implantation-capable embryos.

Microfluidics has the potential to be revolutionary, making the in-vitro experience for the embryo more like the one nature designed.

 

References:

Nir, A. (2002) The fertilization dance: a mechanical view of the egg rotation during the initial spermatozoa-ovum interaction. J. Theor. Biol., 214, 171-179,

Croxatto, H.B. (2002) Physiology of gamete and embryo transport through the fallopian tube. Reprod. Biomed. Online, 4, 160-169.

Ronald S.Suh, Nandita Phadke, Dana A.Ohl Shuichi Takayama and Gary D.Smith. (2003) Rethinking gamete/embryo isolation and culture with
microfluidics Human Reproduction Update, Vol.9, No.5 pp. 451-461.

© 2012, Carole. All rights reserved.

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